Based on 25 years of experience saving clients energy dollars (this includes more than 500 energy cost reduction audits and projects), here are 20 tips for reducing fuel costs in ovens and furnaces
TUNE THAT BURNER
(1%-3% of fuel use)
This is often one of the most valuable steps you can take in reducing fuel costs. Its certainly the easiest. Most tuning sessions require less than a day per unit and return many times the cost of the visit in less than a year.
REDUCE AIR INFILTRATION
2%-5% of fuel use)
Air movement through a process oven or furnace and even a large field-erected boiler can make for significant fuel loss. We use tools like infrared analysis to identify where heat is being lost through a boiler, furnace or oven. This is often a matter of closing up openings with insulation blankets and or making minor repairs at just the right spots.
LINKAGE LESS CONTROLS
(1%-3% of fuel use)
Linkages only allow for limited tuning capability of combustion equipment. In most cases low fire or some other firing rate point gets sacrificed. The answer is a change to the control strategy where you have an actuator installed for both the gas and the air. This allows for much more precise control of fuel air ratios.
ADD OXYGEN TRIM CONTROLS
This involves the addition of a probe to the stack that can measure the excess air use at a particular firing rate. It communicates to the fuel air controls and allows this important parameter to be optimized. It can only be done where the control of fuel and air are separate or where there is a stack damper.
PULSE FIRING CONTROLS
Process oven or furnace burners operate more efficiently when they can run at high fire in an optimized condition. Instead of running at some turndown condition this strategy allows the burners to operate at high fire but in a pulsed condition to get the turndown required. This requires specially designed fuel trains and high cycle rate fuel control valves.
MORE EFFICIENT BURNERS
(2%-5% savings)
In many cases, the efficiency you are getting is limited by the very basic nature of the burner you are using. You can only get so much speed out of a golf cart. You might, for example, have a fixed excess air style of burner that was installed when fuel was cheap.
ADD HEAT RECOVERY
(3%-6% savings)
There may be an opportunity to use heat from the flue gases to do other useful things at your site. These things can include preheating combustion air, feed water, and or even materials that are about to head into an oven or furnace.
DRYERS/DRYING OVEN CONTROLS
(3% to 6% savings)
How are the dryers set up? Are they controlling just on dry bulb temperature? Are relative humidity sensors installed? Does the algorithm consider outside ventilation air humidity? How is your drying cycle set? What is your temperature set point and why? What does it need to be?
EVALUATE OVEN HEAT DISTRIBUTION
(2% to 5% savings)
Its possible that the temperature distribution inside the oven or furnace is horrible for a number of reasons. These could include blocked ducts, recirculation fans not working, and or poor burner adjustments or conditions. This can be evaluated with a furnace survey we can conduct. If this is the case you could be controlling to some parameter that makes no sense and is wasting a lot of fuel.
REVIEW THERMAL OXIDIZER AND OVEN TEMPERATURE CONTROL SETTINGS/TUNING
(2%-4% savings)
Look carefully at the temperature recorder from your thermal oxidizer. If its got a deep saw tooth pattern you are most likely in need of tuning your digital temperature controller. Its obviously over shooting and wasting fuel.
CONSIDER OVEN PRESSURE CONTROLS
3% to 6% energy savings)
Ovens and furnaces with issues such as combined flues, tall flues, and/or exhaust fans can draw room air through places you dont want it to go. Draft or suction in the furnace or oven needs to be precisely controlled for optimizing energy efficiency. This can be done with pressure controls and stack dampers.
CAREFULLY CONTROL VENTILATION AIR
(4% to 8% energy savings)
Ventilation air is what is required to remove moisture and/or contaminants in an oven or furnace. You have to be very careful with this. If its a class A oven it has to not allow the LEL, (lower explosive limit) in the oven get to 25%. However, any more air than this is pure waste. Measure the air flows and help to optimize this issue.
VERIFY THAT FUEL TRAIN VENT VALVES DO NOT LEAK
(Worth thousands if and when you find one!)
We find about 1 in every 50 vent valves in double block and bleed fuel train systems are leaking through when the unit is firing. This often puts thousands of dollars worth of fuel up onto the roof or out a side wall of a building. This is usually a less-than-$500 fix to save thousands. This issue can be found in less than 30 seconds. Heres how. Simply take a latex glove to where these vents are, (usually a 1″ to 2″ pipe terminating on the roof). Hold it over the end for about a minute. If you smell gas and see the glove filling you know you have a leaker. Be careful if you smell gas when doing this. You could be exposed to a hazardous situation.
EXAMINE OVEN/DOOR SEALS
(1%-2% energy savings)
I hate to walk into a plant and see burned up door seals and or product staining on the oven side. It means that heat is being lost through these door seals. We have ultrasonic equipment that is great for finding loose doors. This is not rocket science. Its really a simple maintenance issue but an important one.
CONSIDER OVEN INSULATION/REFRACTORY UPGRADES
(1%-3% energy savings)
If youve got skin temperatures over 160 degrees Fahrenheit you have a problem. First of all it might be an OSHA burn hazard issue. Besides this, you may be losing lots of heat. Consider looking at a refractory or insulation upgrade.
KEEP HEAT TRANSFER SURFACES CLEAN
(2%-6% energy savings)
Sooting happens! In some cases, especially if youve got heat recovery coils installed, things get dirty. Your heat transfer efficiency declines a lot even with a 1/16″ of soot or dust coating. If youve not had things opened up for a good brushing in a while its probably a time issue.
CAREFULLY MANAGE LOADS
(Baskets/Cycle Times/Full Loads/open/Unloading Cycles)
(2%-5% energy savings)
Small loads, heavy baskets and dunnage, and long loading cycle times where furnaces or ovens are sitting there idling, make for considerable waste. Think about what you can do to minimize these wasters. In some cases PLC codes can be rewritten or modified to change these parameters.
EVALUATE WEEKEND SHUTDOWN/START-UP CYCLES
(Nothing saves you more than shutting something off.)
Some people do things like start on a Sunday afternoon to get things warmed up for Monday. How many hours of warm-up do you really need? Have you actually studied it or are you operating on an old paradigm? We have temperature recorders to help you figure out how much of a heat-up you really need.
REVIEW THERMAL OXIDIZER AIR FLOWS
(2%-6% energy savings)
Do you really need to send all of that air to the thermal oxidizer? Do the flows still make sense? Has anything changed? The load in a thermal oxidizer is directly proportional to the amount of air being sent there.
CONSIDER A TECHNOLOGY CHANGE
(10%-30% energy savings)
If youve got a thermal oxidizer or afterburner consider investing in a regenerative unit that swaps heat back and forth to a recovery chamber and cuts your fuel use in more than half. If youve got old fire tube or water tube boilers consider the newest generation of steam generators. They can cut traditional boiler fuel costs by 15% to 20%. There are also many other technologies related to ovens and furnaces which might have you throwing stones in the global manufacturing war when your competitors are using nuclear weapons.
